Change Details

This is an early WIP of the GLX backend. I go through that with a chainsaw
at the moment and hope for some feedback by people knowing all the history
about it and stop me before accidentally cutting off the branch we are
sitting on. ;)
###Overall goals:
* Make the code less convoluted.
* Sync paint with vblanks if extensions required for that are available
* Reduce delay by pushing paint to end of vblank cycle, see [1].
###Currently doing:
* Remove triple buffering. A compositor does not need this when it doesn't
screw up in some other way.
* Remove vsync option. Always sync with vblanks.
* Replace GLX_MESA_, GLX_EXT_. and GLX_SGI_swap_control with
GLX_OML_sync_control only, since this is the standard nowadays and we
don't need to optimize for every legacy X device in the world.
* Remove blocksForRetrace, instead use the Intel swap event or glFinish
to sync with vblank. glFinish should block till vblank, see [2][3].
* In endRenderingFrame don't present a second time. Why was it there in the
first place?
Added 19-08-13:
* When swap events are available don't use the fallback timer.
* Delay timer reduces latency between paint and vsync
###Open questions:
* Is glFinish really blocking till vblank? X Present extension provides events
to get notified about vblank, but since we channel through GLX this is not
available directly to my knowledge. So it's kind of weird that there is only
the Intel swap event to wrap that behavior explicitly.
* Compositor has a compositing timer. It seems we always wait for it, but if
we sync with vblank there is no reason to do it this way. Instead only use
is as a fallback in case sync with vblank is not supported?
[1] https://ppaalanen.blogspot.com/2015/02/weston-repaint-scheduling.html
[2] https://www.khronos.org/opengl/wiki/Swap_Interval
[3] https://github.com/tildearrow/kwin-lowlatency#background

This is an early WIP of the GLX backend. I go through that with a chainsaw
at the moment and hope for some feedback by people knowing all the history
about it and stop me before accidentally cutting off the branch we are
sitting on. ;)
###Overall goals:
* Make the code less convoluted.
* Sync paint with vblanks if extensions required for that are available
* Reduce delay by pushing paint to end of vblank cycle, see [1].
###Currently doing:
* Remove triple buffering. A compositor does not need this when it doesn't
screw up in some other way.
* Remove vsync option. Always sync with vblanks.
* Replace GLX_MESA_, GLX_EXT_. and GLX_SGI_swap_control with
GLX_OML_sync_control only, since this is the standard nowadays and we
don't need to optimize for every legacy X device in the world.
* Remove blocksForRetrace, instead use the Intel swap event or glFinish
to sync with vblank. ~~glFinish should block till vblank, see [2][3].~~ (doesn't seem to be true per se, maybe driver dependent)
* In endRenderingFrame don't present a second time. Why was it there in the
first place?
Added 19-08-13:
* When swap events are available don't use the fallback timer.
* Delay timer reduces latency between paint and vsync
Added 19-08-20:
* Move `present` to `endRenderingFrame` to have less than one frame of latency.
###Open questions:
* Is glFinish really blocking till vblank? X Present extension provides events
to get notified about vblank, but since we channel through GLX this is not
available directly to my knowledge. So it's kind of weird that there is only
the Intel swap event to wrap that behavior explicitly.
* Compositor has a compositing timer. It seems we always wait for it, but if
we sync with vblank there is no reason to do it this way. Instead only use
is as a fallback in case sync with vblank is not supported?
[1] https://ppaalanen.blogspot.com/2015/02/weston-repaint-scheduling.html
[2] https://www.khronos.org/opengl/wiki/Swap_Interval
[3] https://github.com/tildearrow/kwin-lowlatency#background

This is an early WIP of the GLX backend. I go through that with a chainsaw
at the moment and hope for some feedback by people knowing all the history
about it and stop me before accidentally cutting off the branch we are
sitting on. ;)
###Overall goals:
* Make the code less convoluted.
* Sync paint with vblanks if extensions required for that are available
* Reduce delay by pushing paint to end of vblank cycle, see [1].
###Currently doing:
* Remove triple buffering. A compositor does not need this when it doesn't
screw up in some other way.
* Remove vsync option. Always sync with vblanks.
* Replace GLX_MESA_, GLX_EXT_. and GLX_SGI_swap_control with
GLX_OML_sync_control only, since this is the standard nowadays and we
don't need to optimize for every legacy X device in the world.
* Remove blocksForRetrace, instead use the Intel swap event or glFinish
to sync with vblank. ~~glFinish should block till vblank, see [2][3].~~ (doesn't seem to be true per se, maybe driver dependent)
* In endRenderingFrame don't present a second time. Why was it there in the
first place?
Added 19-08-13:
* When swap events are available don't use the fallback timer.
* Delay timer reduces latency between paint and vsync
Added 19-08-20:
* Move `present` to `endRenderingFrame` to have less than one frame of latency.
###Open questions:
* Is glFinish really blocking till vblank? X Present extension provides events
to get notified about vblank, but since we channel through GLX this is not
available directly to my knowledge. So it's kind of weird that there is only
the Intel swap event to wrap that behavior explicitly.
* Compositor has a compositing timer. It seems we always wait for it, but if
we sync with vblank there is no reason to do it this way. Instead only use
is as a fallback in case sync with vblank is not supported?
[1] https://ppaalanen.blogspot.com/2015/02/weston-repaint-scheduling.html
[2] https://www.khronos.org/opengl/wiki/Swap_Interval
[3] https://github.com/tildearrow/kwin-lowlatency#background